One possible reason could be that Naruto realizes Sakura's unrequited love for Sasuke. He might feel tired of always being in a one - sided emotional situation with her. Another reason could be that Naruto has his own goals and growth to focus on. His journey to become Hokage and protect the village requires all his attention, leaving little room for his previous feelings for Sakura.
One possible reason could be that Naruto has finally realized that Sakura's heart has always been with Sasuke. After years of chasing after her and getting constantly rejected or overlooked, he just gets tired and decides to move on. He might start to focus more on his own personal growth and the other relationships in his life that are more reciprocal.
Perhaps the story then delves into Naruto exploring new love interests. He may meet a girl who shares his values and dreams more closely. Meanwhile, Sakura might start to realize what she has lost in Naruto. This could lead to some tension or even a new dynamic between them where Sakura tries to win back Naruto's attention but he is no longer interested.
Well, it makes the triangle less of a love triangle. With Naruto out of the picture in terms of caring for Sakura, it becomes more about Sakura and Sasuke's relationship without Naruto's interference. Sasuke may not have to deal with Naruto's rivalry in terms of Sakura's affection anymore.
One possible reason could be that Naruto has faced too many betrayals. Maybe his friends turned on him in the fanfic, which made him lose faith and stop caring.
I'm not sure specifically as there could be many different takes on it. It might be a fanfiction where the character Izuku reaches a point of apathy or stops caring about things he previously held dear, like his dreams of becoming a hero or his relationships. It could be due to some traumatic event or a slow build - up of disappointments in the story's universe.
One possible reason could be that Naruto has faced so many betrayals and hardships in the fanfiction. For example, if his friends turned on him for some contrived reasons, it might lead him to stop caring. Another reason could be the constant failure in achieving his goals, like protecting the village but always being undermined by political intrigue within the fan - made story.
It could be that Naruto has outgrown his initial feelings. As he matures, he starts to view Sakura more as a friend. In the fanfic, his experiences in the ninja world might have changed his perspective on love. He might have seen so much pain and sacrifice that he no longer wants to hold on to a love that might be one - sided or not as fulfilling as he once thought. Also, Sakura's continued love for Sasuke in the fanfic could be a factor that makes Naruto step back.
One example is when Sasuke gives Sakura a special item in a fanfic. It could be a charm that has some significance to him, which shows he is thinking about her. Another example is that he might train with her more closely than others. This is not only to improve her skills but also because he wants to be near her.